This project is designed to provide information on the electrophysiological and morphological properties of alpha motoneurons and of the muscle fibers (muscle units) innervated by them. The properties of gamma motoneurons are also being investigated. Methods include electrophysiological techniques of intra- and extracellular recording, mechanical recording of muscle unit properties, neuroanatomical techniques of intracellular injection of horseradish peroxidase to label individual, functionally identified motoneurons, retrograde transport of lectin-conjugated horseradish peroxidase to label motor nuclei, and computer modeling studies to analyze the experimental data produced. Recent work has emphasized detailed analysis of the dendritic morphology of alpha- and gamma-motoneurons, with development of a computer model to describe the structure of these dendrites using a minimum number of parameters.